1. Field of the Invention
The present invention relates generally to the field of optical fiber communication and in particular to the optical amplifier.
2. Description of the Related Art
The optical amplifiers are widely used in wavelength-division multiplexed (WDM) optical communication systems and networks. In such systems and networks, the available transmission band for WDM channels depends mainly on the characteristics of the optical amplifiers. It is desirable the optical amplifiers to have wider bandwidth to increase the capacities of the WDM systems and the WDM networks. Thus there have been many efforts to implement wide band optical amplifiers.
FIG. 1 shows an example of conventional wide band optical amplifier proposed in a paper of S. Aisawa, T. Sakamoto, M. Fukui, J. Kani, M. Jinno, and K. Oguchi, Ultra-wideband, long distance WDM demonstration of 1 b/s (50xc3x9720 Gbit/s), 600 km transmission using 1550 and 1580 nm wavelength bands, Electron. Lett., vol. 34, no. 11, pp. 1127, 1998. The optical amplifier of FIG. 1 is realized by combining two braches of muti-stage optical amplifier sections in parallel. The signals that entered the amplifier through the input port (P1) are first split into two sub-band signals (C-band and L-band signals) by a wavelength-division multiplexer (WDM). The C-band signals enter the upper branch section, whereas the L-band signals the lower branch section. The upper branch section is composed of two erbium-doped fiber amplifiers (EDFAs) and a mid-state device comprising a gain equaling filter (GEQ) and a dispersion-compensating fiber (DCF). The lower branch section is composed of two gain-shifted erbium-doped fiber amplifiers (GS-EDFAs) and a mid-state device. The outputs of both the braches are combined by the other wavelength-division multiplexer (WDM) after passing through optical attenuators (ATTs). The amplifier output signals come out through the output port (P2) of the wavelength-division multiplexer (WDM).
The optical amplifier of FIG. 1 offers a wide bandwidth more than 60 nm in total. However, wide band optical amplifiers with parallel configurations like the optical amplifier described in FIG. 1 are relatively complex and costly since both the branches require their own mid-stage device.
The present invention is contrived in order to solve the above-mentioned problem. It is an object of the present invention to provide a multi-stage wide band optical amplifier. Wherein, (1) the signals that enter the amplifier are split into a couple of sub-band signals and each sub-band signals are amplified independently at different amplification sections. (2) The sub-band signals share a common mid-stage device to reduce the complexity and the cost.
In order to meet the above object, the present invention comprises an optical splitter section, two optical pre-amplification sections, two optical routers, a common mid-stage device, two boost-amplification sections, and an optical combiner section. The common mid-stage device comprises one or more of follows, optical filters for flattening the gain response of the optical amplifiers and suppressing the accumulation the amplifier noise, optical attenuators, and dispersion compensators for compensating for the chromatic dispersion of the optical fibers.